There are two hash functions
implementation
org.elasticsearch.cluster.routing.operation.hash.djb.DjbHashFunction
and org.elasticsearch.cluster.routing.operation.hash.simple.SimpleHashFunction,
default is DjbHashFunction. You can try get the hash by
using DjbHashFunction.DJB_HASH(you id)
On Wednesday, March 26, 2014 9:49:10 PM UTC+11, Han JU wrote:
>
> Thanks for your reply.
>
> As far as I know, in Java, basic hash value of positive int/long value is
> just themselves (our ids are small values like 1125, 345 etc).
> So I calculated some_id % 128, and I got 116 distinct values. But in
> reality there's a lot less shards in use.
>
> Does ElasticSearch use some special hash function?
>
> 在 2014年3月26日星期三UTC+1上午11时39分15秒，Kevin Wang写道：
>>
>> ES will get the shard id by hash(routing)%num of shards, in your case,
>> there are only 167 distinct values but have 128 shards, I think it's highly
>> possible there is less than 128 distinct hash values. So some of the shard
>> will not have any data.
>>
>>
>> Kevin
>>
>> On Wednesday, March 26, 2014 9:30:36 PM UTC+11, Han JU wrote:
>>>
>>> Hi,
>>>
>>> We've indexed 25M documents into a single index of 128 shards with 1
>>> replica.
>>> The `routing` parameter is set to a path in the document, which is an
>>> int value:
>>>
>>> _routing: {
>>> path: "some_id"
>>> required: true
>>> }
>>>
>>>
>>> In out 25M documents, there's 167 distinct values of this "some_id" and
>>> in our expectation, ElasticSearch will route these documents evenly across
>>> all shards.
>>> But we've found out that, out of 128 shards, there are 53 empty shards
>>> (with 0 document inside), or, 40% of the shards are not used at all.
>>>
>>> My question:
>>>
>>> - is this normal? Do we miss something in configuring routing?
>>> - does this imbalanced shard utilization affect indexing speed?
>>>
>>> We can confirm that all documents are correctly indexed and routing
>>> works (when searching with routing only 1 shard responds with the correct
>>> answer).
>>> ElasticSearch version is v1.0.1.
>>>
>>>
>>> Thanks!
>>>
>>
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